The goal of this renewal grant is to translate our pioneering studies on the biology of bone morphogenetic protein-15 (BMP-15) in rodents to the human. The rationale underpinning the grant is that mutations in the bmp15 gene cause infertility in women due to defects in folliculogenesis. BMP-15 has a critical physiological role in regulating granulosa cell proliferation and differentiation in women. At present, almost nothing is known about how BMP-15 acts to control human granulosa cell function. We have recently identified posttranslational modifications in the primary structure of recombinant human BMP-15 (rhBMP-15) by proteomics analysis, most notably a phosphorylation in the mature region. Importantly, phosphorylation is essential for the bioactivity of rhBMP-15. Interestingly, de-phosphorylated rhBMP-15 can negate the bioactivity of phosphorylated rhBMP-15. Moreover, de-phosphorylated rhBMP-15 also inhibits the bioactivity of recombinant human growth and differentiation factor-9 (rhGDF-9) and rhBMP-7 that share a common BMP type II receptor with rhBMP-15. However, de-phosphorylated rhBMP-15 does not impair the bioactivity of rhActivin A, which shares neither type I and type II receptors with rhBMP-15. The hypothesis that emerges from these novel findings is that protein phosphorylation of BMP-15 may represent a primary physiological determinant for ovarian function and fertility in women, and that the non-phosphorylated BMP-15 may be a functional antagonist for not only BMP-15 but also for other selective members of the TGF-? superfamily. Four Specific Aims are proposed to test these hypotheses. Aim 1: Determine the biological function of rhBMP-15 in human granulosa cells at defined stages of follicle development. Aim 2: Establish the role of phosphorylation in the bioactivity of rhBMP-15 in human granulosa cells. Aim 3: Investigate the molecular and cellular mechanisms by which non-phosphorylated rhBMP-15 antagonizes broadly the activity of selective BMP/GDF ligands. Aim 4: Determine the biochemical characteristics and the biological functions of the BMP-15 mutants identified in premature ovarian failure (POF) patients and explore to what extent the mutations are functionally associated with the phenotype of POF patients. The proposed studies should provide significant advances in understanding the regulatory mechanisms of follicle growth and development by the oocyte-specific factor, BMP-15, and could hold promise for new strategies for the treatment of infertility and regulation of fertility in women. PUBLIC HEALTH RELEVANCE: Bone Morphogenetic Protein-15 (BMP-15) is a critical growth factor that controls ovarian follicle growth and development, leading to the normal ovulation, thus, female fertility. In this grant application, we propose to uncover the biological functions of BMP-15 and the underlying molecular mechanism in the human ovary. The proposed studies should provide significant advances in understanding the regulatory mechanisms of follicle growth and development by BMP-15, and ultimately develop new regimens for the treatment of infertility and regulation of fertility in women.